One example of known electric wire connection devices is shown in Patent Document 1 (JP 2003-230214A). In this device, an electric wire group is passed in a sealed state through a hole that penetrates a wall. In particular, a grommet through which the electric wire group (wire harness) is inserted is attached to the wall provided with a through hole, and a flexible lip having a large diameter that is provided in the grommet is brought into elastic contact with the periphery of the through hole to seal the through hole.